Technology and our changing world high Technology

Review Questions.

1. 
   Name two measuring systems used in this country.
   
2. 
   How many base units are there in the metric system?
   
3. 
   How many millimeters are there in a meter?
   

MEASURING AND MARKING
You must learn to measure accurately in both systems of measurement. Remember the motto. “Measure twice; cut once”. No project will turn out well if you measure incorrectly.
Rules
A bench rule is a wood rule with brass tips on the aids. The brass tips protect the aids from damage. A damaged rule will not measure accurately.
One side is graduated (divided) into eighths of an inch along both edges.
The other side is graduated in sixteenths of an inch. Bendi rules are made in 1’ (12”), 2’ (24”), and 3’ (36”) lengths. Sometimes the3’ rule is called a yardstick. Metric ben ch rules are also available.
The zigzag rule, or folding rule, is used to measure longer stock when very exact measurements are not too important.
The push-pull, steel tape, or rape rule is a, metal rule that rolls up into a case. Thae is a hook at the end to slip ova the edge of the board. Since it is flexible (bends easily) it can measure curved surfaces. It is also very good for measuring the inside diameter of things.
Squares
The try square is used for squaring, measuring, and testing. The blade and handle are at right angles (90°Q to each other. The try square is used:
• To test wh eth er a surface is flat.

• 
  To check a face and edge surface for square-ness.
  
• 
  To mark lines across lhe face or edge of stock. There are graduations along the edge for measuring. Never use the tool for pounding or hammering.
  

The combination square can do many things. Square can do many things. This tool has a blade and a head. The blade has a groove cut along its length so that it can slide into the head. One side of the head makes 90°. angle with the blade and the other side a 45° angle. There is a level (a tool for testing for a flat, horizontal surface) in the head. The combination square can be used as:

• 
  A try square.
  
• 
  A miter square to lay out45° angles and check them.
  
• 
  A dep Di gauge.
  
• 
  A lev el.
  

The steel square is L-shaped like the fry square but larger. It has a body (the longer part) and a tongue (toe shorter part). The steel square is used for measuring and checking.
The carpenter’s square is also called a framing square. It is a large steel square used for measuring and laying out. The body is 2” x 24” and toe tongue is ‘А” X 16”. The tables of figures on this square are useful to toe carpenter.